1. Field of the Invention
The present invention relates to an implementation method of all-optical half adder by using semiconductor optical amplifier (SOA)-based devices and the apparatus thereof. In more detail, it relates to an implementation method of all-optical half adder comprising an all-optical XOR gate and an all-optical AND gate, implemented by using SOA-based devices, and an apparatus thereof.
2. Description of the Related Art
Demand of high-speed and large-scale of a communication system is recently being increased, however, most of currently used communication systems based on silicon (Si) material (i.e. based on electric signal) have limitations in their operation speed and information handling capacity. And thus, the future performance of this type of communication system is questionable.
On the other hand, a communication system using optical devices based on indium phosphide (InP) can solve the problems of operation speed and information handling capacity described above.
Generally, a communication system is constituted by integrating various single gates such as AND, OR, XOR, NAND, NOR, and NXOR. And, so is the communication system using optical devices. As the complexity of the communication system increases, the multiple operations of logic gates are required.
A half adder is a basic example of a communication element carrying out the complex and multiple operations.
A half adder is a computation element in which both an XOR logic operation and an AND logic operation are being carried out simultaneously.
Recently, many researches are being concentrated on the development of XOR gates such as an XOR using an ultrafast nonlinear interferometer (UNI)(C. Bintjas, M. Kalybas, G. Theophilopoulos, T. Stathopoulos, H. Avramopoulos, L. Occhi, L. Schares, G. Guekos, S. Hansmann and R. Dall""Ara, IEEE Photonics Technology Letters, vol. 12, no. 7, pp. 834-836, 2000), an XOR using a terahertz optical asymmetric demultiplexer (TOAD)(Pousite, Blow, Kelly, Manning, Opt. Commun., 156, pp. 22-26, 1998), an XOR using a Sagnac gate (T. Houbavlis, Zoiros, A. Hatziefremidis, H. Avramopoulos, L. Occhi, G. Guekos, S. Hansmann, H. Burkhard and R. Dall""Ara, Electronics Letters, vol. 35, no. 19, pp. 1650-1652, 1999) and an XOR using an interferometric wavelength converter (IWC) (T. Fjelde, D. Wolfson, A. Kloch, B. Dagens, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt and M. Renaud, Electronics Letters, vol. 36, no. 22, pp. 1863-1864, 2000).
Various researches have also been made on AND gates such as an AND using an electro-absorption modulator (EAM) (E. Awad, P. Cho and J. Goldhar, IEEE Photonics Technology Letters, vol. 13, no. 5, 2001), an AND using a nonlinear optical loop mirror (NOLM) (B. Olsson and P. Andrekson, Optical Fiber Communication Conference and Exhibit, Technical Digest, pp. 375-376, 1998) and an AND using a four-wave mixing (D. nesset, M. C. Tatham and D. Cotter, Electronics Letters, vol. 31, no. 11, pp. 896-897, 1995).
Logic gates using a UNI, a TOAD, or a Sagnac gate as described above have an advantage of high operation speed. However, the key components of these systems are optical fibers that are complicated and hard to be integrated with other devices, and thus, they have difficulties in being applied to an optical computation system requiring a highly integrated circuit.
And, an implementation method using a four-wave mixing has a problem that it is hard to control the polarization state of a signal.
Compared with these systems described above, optical gates using a single semiconductor optical amplifier (SOA) have advantages that they are stable, providing a small system size, easy to be combined with other optical devices, and providing a possible polarization- and wavelength-independency (Fjelde, Wolson, Kloch, Janz, Coquelin, Guillemot, Gaborit, Poingt, Dagens and Renaud, Electronics Letters, vol. 36, no. 9, 2000).
The present invention is proposed to solve the problems of the prior art mentioned above. It is therefore the object of the present invention to provide an implementation method of all-optical half adder by using SOA-based devices, which is stable, providing a small system size, easy to be combined with other optical devices, and providing a possible polarization- and wavelength-independency, by implementing an all-optical XOR gate using the cross-gain modulation (XGM) characteristic of SOA and an all-optical AND gate using a SOA-based cross-phase modulation (XPM) wavelength converter, and an apparatus thereof.
To achieve the object mentioned above, the present invention presents an implementation method of all-optical half adder by using SOA-based devices characterized in that SUM signal is outputted by adding the output signals of the XGM characteristics produced by gain-saturation and wavelength conversion of two semiconductor optical amplifiers (SOAs) by injecting both pump signal and probe signal together into each SOA in the different way; and CARRY signal, of which the power of output signal is being increased by simultaneously injecting a high-power probe signal into an XPM wavelength converter with varying a pump signal and the power of output signal is being decreased by simultaneously injecting a low-power probe signal into an XPM wavelength converter with varying a pump signal, is outputted.
To achieve the object mentioned above, the present invention presents an all-optical half adder comprising: a fiber ring laser and a pulse generator for generating a pulse signal having a certain interval; a coupler for being injected by a pulse signal and dividing the injected pulse signal; an optical delay for delaying one part of divided signal; a coupler for producing an A-signal having 1100 pattern by combining the delayed signal and the other part of divided signal; an optical delay for producing a B-signal having 0110 pattern by delaying the A-signal; the first semiconductor optical amplifier (SOA1) for being injected by A-signal as a probe signal and B-signal as a pump signal and outputting a Boolean A{overscore (B)} logic signal; the second semiconductor optical amplifier (SOA2) for being injected by A-signal as a pump signal and B-signal as a probe signal and outputting a Boolean {overscore (A)}B logic signal; and a cross-phase modulation (XPM) wavelength converter for simultaneously being injected by A-signal and B-signal and outputting a logic signal having 0100 pattern.
An all-optical XOR gate in accordance with the present invention is implemented by using the XGM characteristics of two semiconductor optical amplifiers (SOAs). As seen in the experimental setup, it is independent of a clock signal and/or a CW signal since the XOR gate uses only input signals A and B.
Therefore, as long as the speeds of A-signal and B-signal, which are inputted into the two semiconductor optical amplifiers (SOAs), are the same, an element can be implemented without a clock signal and/or a CW signal.
In addition, an XOR gate in accordance with the present invention firstly produces a Boolean A{overscore (B)} signal and a Boolean {overscore (A)}B signal, and summates them thereafter. Therefore, various logic signals can be generated by using only one all-optical XOR gate since A{overscore (B)} signal and {overscore (A)}B signal can be separated.